Note: Descriptions are shown in the official language in which they were submitted.
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FLOATING COATING DIE MOUNTING SYSTEM
TECHNICAL FIELD
The present invention relates to coating dies.
More particularly, the present invention relates to
10 supports for coating dies.
BACKGROUND OF THE INVENTION
Coating dies are well known, and there are many
variations. One typical coating die includes an
15 upstream bar and a downstream bar connected together.
An upstream die lip is part of the upstream bar, and a
downstream die lip is part of the downstream bar. A
manifold is formed in one or both bars and leads into a
slot which exits the die at the lips of the die.
20 Coating fluid is supplied through a channel to the
manifold for distribution through the slot and coating
onto a moving web or other surface to be coated. The
coating fluid can form a continuous coating bead among
the upstream die lip, the downstream die lip, and the
25 surface being coated (such as a moving substrate or
web). The coating fluid can be one of numerous liquids
or other fluids. A vacuum chamber can apply vacuum
upstream of the bead to stabilize the coating bead.
The coating fluid can be applied to the web in a free
30 span or against a backup roller.
A wide range of fluids are applied to surfaces
using various coating dies. The coating dies
themselves are modified for a specific application to
optimize the coating of fluid on the surface. Varying
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other external features, such as the hardness of backup
rolls, can also optimize coating. Within a given die
configuration, the coating quality can be changed
drastically by making small angle changes and height
changes between the coating die parting line and a
radial line extending outward from the center of the
backup roll. Still, uneven coating persists often due
to such factors as rubber roll runout or straightness,
web line vibration, web thickness and surface
variations, nonlinearity of the die lips, and the need
for a precise placement of the die lip on the web.
Coatings are sometimes inconsistent across their width
due to an unevenness of the cross web die pressure.
The mounting systems for the coating dies are also
modified to optimize coating. Coating dies are mounted
at a location, sometimes called the coating station, at
which the coating fluid is to be applied to a surface.
Known mounting devices are rigid or fixed. That is,
the die is positioned and fixed at a precise location
adjacent the surface to be coated to optimize coating.
This location can be changed to accommodate various
fluids and coating conditions. However, during
coating, the die remains stationary on its mount.
In some cases, coatings are applied to the web
without any supporting member on the web backside at
the point of coating application. An example of this
is mayer rod coating where the web is supported between
two rollers and a coating rod is mounted such that the
web partially wraps around the rod circumference. The
coating uniformity is controlled by, among other
things, the rod straightness, web wrap angle around the
rod, overall web tension, and the point-to-point web
tension uniformity. If there is bag in the web at any
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point, that part of the web will have heavier coating
than an adjacent area without bag that has a higher
corresponding web tension.
In a similar manner, a pre-metered coating die can
be pressed against a web in a free span between two
rollers. Assuming that the coating die is designed
properly for the coating liquid and provides a
perfectly uniform crossweb distribution without the web
in place, the final coating uniformity is a function of
the localized web tension. A high web tension in one
area of the die will cause the liquid to move towards
an area having a lower localized web tension. Lower
localized web tension in coating areas have higher
coating thicknesses and higher tension areas have lower
i5 coating thicknesses. In extreme cases, the web tension
will dominate the coating quality and cause skips and
streaks.
U.S. Patent No. 3,854,441 teaches using a press
roll to apply force from the backside of the web
against the die lips and the fluid exiting the die
slot. Pneumatic cylinders provide pressure against the
web and lift the press roll away from the web.
However, very light pressures can not reliably be
obtained because of friction in pneumatic cylinders
sized to lift the weight of the roll.
GB Patent Publication No. 1190324 illustrates the
use of a flexible blade to apply pressure between the
web and the coating die. This is capable of very low
pressures depending upon the flexibility of the blade.
However, the blade rubs against and may scratch the
web.
U.S. Patent No. 3,609,810 discloses die coating
where air lift bellows push and hold in position the
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die and its knife bar in close proximity to the web on
a back-up roll. The gap between the die lip is fixed
by pushing the die and the mounting fixtures against
stops which may be adjusted to adjust the gap. With
this arrangement, if the back-up roll is not perfectly
round the gap will vary with each revolution. Urging
the die against fixed stops does not allow self-
compensation for out-of-roundness. Nor does it
compensate for variation of the web thickness which
will vary the gap.
Streaking can be more common when using contact
extrusion die systems {as compared to non-contact
systems) to apply thin coatings or fluids. In contact
extrusion coating, the die position depends on whether
fluid is exiting the die. If no fluid passes through
the die, the die would contact with the substrate.
When fluid passes through the die and exits through the
die slot, the fluid flow causes a hydrodynamic pressure
that moves the die away from the substrate, thereby
opening a gap between the die lip and the substrate.
This gap is known as the separation gap.
This contrasts with the metering gap which is a
set, fixed clearance between a coater component (such
as a knife edge) and the web. It is set by adjusting
and fixing the mounting before coating. Thus, even
when no fluid is being applied, the gap is still there.
When fluid is applied, the gap is still there.
There is a need for a mounting system for a
contact die coater in which the separation gap can be
adjustable during coating to maximize coating quality.
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SUMMARY OF THE INVENTION
An adjustable mounting system for premetered
contact coating dies includes a base and a die-
receiving portion movably connected to the base.
During coating, the die can float a distance from the
surface being coated based on the balance of forces
between the die and the coated surface. This creates a
variable separation gap and allows automatic self-
compensating for variations in web or fluid properties.
This, in turn, optimizes the coating characteristics,
by precisely varying the position of the die-receiving
portion in the vicinity of the surface to be coated.
The die-receiving portion can be connected to the
base by either a flexible member or a precision hinge
member .
The movement of the die-receiving portion can be
limited by a stop mechanism. The die can be permitted
to float by pressing between the coating die and the
base, pressing against the coating die, the die-
receiving portion, and the flexible member, as well as
pressing between the die-receiving portion and the
base, pressing between the flexible member and the
base, and pressing between the flexible member and the
stop mechanism.
The base can include a lower portion and a leg
portion, and the die-receiving portion can include a
mounting portion and a leg portion rigidly connected to
each other. The base leg portion can be generally
parallel to the die-receiving portion leg portion. The
die-receiving portion can also include a force-
generating arm rigidly connected to the leg portion.
In another embodiment, the mounting system can
also include an enclosure for protecting at least the
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flexible member and the fluid-loaded bladder used to
position the die. The enclosure and the force-applying
arm of the die-receiving member can each have openings
to receive a fluid feed conduit for feeding fluid to
the die. Alternatively, the die receiving portion can
be shaped to shield the fluid-loaded bladder used to
position the die and the flexible member by serving as
an enclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side view of a mounting system of
one embodiment of the invention.
Figure 2 is a top view of another mounting system
of the invention.
15 Figure 3 is a side view of another mounting system
of the invention.
Figure 4 is a perspective view of another mounting
system of the invention.
Figure 5 is a side view of another mounting system
of the invention.
Figure 6 is a side view of another mounting system
of the invention.
DETAILED DESCRIPTION
The invention is a mounting system for premetered
contact coating dies, such as extrusion and slot dies
that apply a premetered amount of coating onto a
surface. (This is contrasted with, for example, blade
coating, which applies an excess of coating which is
removed during the coating process.) The inventors
have found that die mounts which position the coating
die in the vicinity of the web (or other surface being
coated), and in which the force of the die against the
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web can be precisely adjusted during coating, to
significantly improve coating. The mounting system
permits the die to float on the coating. The mounting
system can reliably and repeatably position the die to
apply a consistent force against the web.
In contact coating with the mounting system, the
die position depends on whether fluid is exiting the
die. As fluid exits through the die slot, the fluid
flow causes a hydrodynamic pressure that moves the die
away from the substrate, thereby opening a separation
gap between the die lip and the substrate. The
mounting system allows setting a desired pressure
between the fluid coated on the web and the die by
applying consistent low forces (based on the fluid
rheology) to the die sufficient to coat a fluid on the
web. The mounting system improves upon known systems
in that it can "float." It allows the die to move
toward and away from the web as variations in the web
or in the coating fluid pass by the die. The die moves
toward the web by the applied pressure from the
mounting system and the die moves away from the web in
reaction to forces from the coated web. This permits
the applied coating to be more uniform and to achieve
the desired characteristics.
In response to variations in the web location or
web thickness (such as splices), the mounting system
can move the die to adjust the force and yield the
desired coating appearance. As the force of the die
against the fluid changes, the web, whether supported
or in free span, counteracts the die force to permit
the die to float to apply the appropriate force against
the web to yield the desired system equilibrium.
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The mounting system can apply a consistent light
force of approximately 15 to 30 gm/mm of die width
against the web. This preload is held constant in..
response to variations such as web thickness, roll
runout and machine vibrations that would disturb the
gap between the die and the web. This allows an
operator, while coating, to precisely oppose the
hydrodynamic force created by fluid flowing through the
gap that would otherwise further separate the die from
the web. Maintaining this constant preload helps yield
the desired coating appearance.
For a coating system, the applied fluid pressure
can deform the substrate or the applicator. This
alters the fluid flow, and changes the localized
hydrodynamic pressure that acts on the web or the
applicator. This competition between the hydrodynamic
and the elastic restoring forces of the deformable
walls of the channel that confine the fluid is
described by the theory of elastohydrodynamics. (To
develop a hydrodynamic pressure in free span, a die
with the appropriate lip geometry is brought into
contact with a tensioned web that bridges the gap
between two parallel rollers. The contact point of the
die must be wrapped by the surface and create ideal
entering and leaving angles between the surface and the
die slot. In this arrangement, web tension determines
the elastic pre-load of the surface side of the
converging channel and low or high tension lanes will
affect the hydrodynamic forces and the appearance of
the coating. In some cases, such as deformed webs
where the edges or interior lanes show bagginess when
the bulk of the web is tensioned and flat, it is
difficult to create an acceptable coating across the
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full die width. This requires constantly adjusting
some die parameters, such as penetration, attack angle,
and span distance, to compensate.) The mounting system
of the invention allows the die to seek a balanced
position that stabilizes the competing forces between
the fluid and the mounting system.
Because the die is relatively unresponsive to the
hydrodynamic and elastic forces, the mounting system
responds to only relatively low frequency disturbances
to the balance of forces, such as trending changes in
web caliper and fluid properties. To counter higher
frequency disturbances, like roll run-out or machine
vibrations, free spans of web or soft roll covers
against which a web is coated can be used to comply and
accommodate these changes. Soft rubber rolls reduce
the impact of non-ideal lanes of tension in the web on
coating quality. When coating against a metal backup
roll, the coating reflected the backup roll surface
imperfections. Like the web in free span, the roll
cover is a low mass system that can quickly react to
forces that lie in the frequency domain of disturbances
that can manifest themselves as visible coating
defects. Combining a floating die system and free span
or soft rubber roll creates an optimum contact die
coating system; one that compensates for both low and
high frequency disturbances.
The adjustment of the die position by the mounting
system can be performed by any known adjusting
apparatus. Biasing devices, like springs, and other
mechanical systems can be used. Pneumatics, including
flexible, fluid-filled containers also can be used
where the dampening of the fluid can be used to
advantage. These systems can be used separately or
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together. Pneumatics allows maintaining the spring
rate and the desired die force at a nearly constant
value even as the stationary part of the mount moves.
"Bladders" will be used to generically describe all
pneumatic versions, such as tubes, and fluid-loaded
diaphragms, which press the die lip against the moving
web. Any fluid can be used, including air. ..
"Flexible" includes both linear and torsional
motion and is preferably elastic. As described, the "x
direction" is the direction describing the coating
thickness, a direction perpendicular to the web. The
"y direction" is the direction describing the width of
the web. The "z direction" is the direction describing
the length of the web. The optimum dimensions,
properties, characteristics, and materials of the
various components of the mounting system depend on
various other parameters such as the die size and mass,
the fluid characteristics, the intended coating
characteristics, and the web features.
Figure 1 shows a parallel knife edge floating
mount having three degrees of freedom (linear
translation in the x and y directions and rotation
about the z axis). One or more mounts can be used to
support the die. In this system 100, a bottom,
stationary plate 102 has a lower surface 104 and an
upper surface 106. A top, moving plate 108 has a lower
surface 110 and an upper surface 112. The die 10 is
bolted or otherwise attached to the upper surface 112
of the top plate 108. That the bottom plate 102 is
"stationary," means that it remains fixed during
coating. It can move to a retracted position, such as
for shutdown, and move to a coating position closer to
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the web for coating, but this movement does not occur
during coating.
The upper surface 106 of the bottom plate 102 and
the lower surface 110 of the top plate 108 each have a
pair of V-shaped grooves 114, 116 respectively, in
corresponding locations. A pair of parallel knife-
edged plates 120 seat in the V-shaped grooves 114, 116
in the upper surface 106 of the bottom plate 102 and
the lower surface 110 of the top plate 108. A tension
spring 122 (or other biasing device) spanning the
bottom and top plates 102, 108 helps keep the knife-
edged plates 120 in contact with the corresponding
grooves 114, 116. The die 10 can be pushed against the
web using a biasing device (not shown in Figure 1) such
as a commercially available stiff-walled air-inflated
rubber bladder, or an air-inflated flattened polyester
tube. This design has very low inherent stiction
(friction that tends to prevent relative motion between
two movable parts at their null position). The
mounting system 100 keeps the die 10 at a constant
angle, and the die elevation changes slightly depending
on where it is in the arc of its stroke. With this
design the die angle can change only if the die
reaction forces cause the knife-edged plates 120 to
lose contact with their corresponding grooves 114, 116.
These die reaction forces are generated by the viscous
drag of the web on the coating fluid which transmits
the force to the die body and will cause the die lip to
tend to move in the same direction as the web.
Another embodiment of the mounting system 200,
shown in Figure 2, is a compound flexure stage system
having one degree of freedom. In this design, a series
of flexible members, such as shim stock plates, are
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located between the stationary, intermediate and
movable members. Alternatively, links with precision
hinges can be used instead of the flexible members.
For example, bronze bushings or ball bearings can be
used.
The system 200 includes a base 202 which is fixed.
An intermediate member 204 is connected to the base 202
by two flexible members 206. A moving member 208 is
connected to the intermediate member 204 by two
additional flexible members 210. This system 200
allows translation along one axis while being rigid
enough to prevent translation along the other two
orthogonal axes or any rotation. The overall stiffness
of the unit can be adjusted by changing the thickness,
length, or material of the flexible members. It can be
operated with or without force generated by a pneumatic
device. When using a rubber tube to increase the
overall spring constant of the device, the operating
position of the stationary part of the mount becomes
more critical. This is because uniform increments of
movement of the stationary reference position toward
the web generate ever increasing increments of force
between the die and the web.
Figure 3 shows a simple flexure stage floating
mounting system having two degrees of freedom (linear
translation in the x and y directions). This
embodiment is similar to that of Figure 1, but
vertical flex members are used instead of knife edged
plates. This mounting system 300 includes a bottom,
stationary plate 302 fixed to a side stationary support
304. A top, moving plate 306 receives a die and is
connected to the bottom, stationary plate 302 by at
least two vertical flex members 308. The middle of
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each flex member 308 can be clamped between a pair of
thicker clamp plates 310 to prevent buckling.
Stainless steel shim stock 0.0254 cm (0.010 in) to
0.0762 cm (0.030in) thick can be used as the flex
members 308. Thicker material also can be used.
A stationary block 312 is mounted on the bottom,
stationary plate 302 between the two vertical flex
members 308. The stationary block 312 serves as a stop
to restrict movement of the clamp plates 310 and the
top plate 306. Other mechanical stops can be used.
At least one fluid bladder 314 is used to adjust
the die 10 position. One or more bladders 314 can be
located between clamp plate 310 closer to the web and
the stationary block 312, or between the clamp plate
310 farther from the web and the side stationary
support 304. As shown, the bladder 314 is located
adjacent the clamp plates 310 at the side opposite the
side stationary support 304. This is the same side as
the die face. In this position, increasing the bladder
pressure moves the flex members 308 and the clamp
plates 310 to move the top plate 306 and the die 10
toward the surface being coated. The bladder 314
(which is 0.005 cm (0.002 in) to 0.008 cm (0.003 in)
thick) had a width of slightly more than 1.27 cm (0.5
in) when flattened and can be ultrasonically bonded
along its major axis with a lap joint. The end also
can be ultrasonically sealed when the tube is
flattened.
If the center of pressure of the bladder 314 is at
the midpoint between the lower and upper flex points of
the flex members 308, the force generating arm is about
half the length of the arm forcing the die against the
web. Thus, the force available to press the die
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against the web, due to the "lever arm ratio" was about
half that generated at the bladder 314. This lever arm
ratio is the effective length of the force-generating
arm divided by the length between its lower flex point
and its top flex point (if there is one) or the die
centerline.
In a modification, a bladder 314 can be located
between the side stationary support 304 and the top
plate 306. Inflating the bladder 314 to increase its
size moves the top plate 306 and the die 10 toward the
surface being coated. The bladder 314 was placed with
its major axis in a horizontal plane between the lower
right vertical surface of the die 10 and the side
stationary support 304. The minor axis was vertical.
This generated adequate die loading for successful
coating at pressures above 50 cm (20 in) to 77 cm (30
in) water. As the gap between the surfaces on each
side of the bladder increased, the minimum required
inflation pressure to achieve good coating also
increased due to the reduced contact area of the
bladder and the adjoining surfaces.
In another modification, multiple flex members 308
can be used. When multiple flex members are clamped
adjacent each other, there is stiction in the mounting
movement, due to the sliding friction force of the flex
members 308 against each other. If the die 10 is
excited into unwanted movements that do not mimic the
web position, the sliding friction from the small
relative shear movement between adjoining flex members
308 can accommodate the die movements. With a bonded
viscoelastic layer of material between adjoining flex
members, changing the position of the viscoelastic
material will also change the degree of dampening.
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The flex members 308 can be pieces of Esterlam
brand doctor blade material (Esterlam International
Limited, Ivybridge, Devon, United Kingdom) 0.061 cm
(0.024 in) thick. Other than a light force due to the
deflection of the flex members, pressurized fluid (such
as air) provides the die loading force. The die height
changes slightly as it moves through its range of
travel, defined by the arcs of the flex members and the
left and right clamp plates. The die angle remains
almost constant in this embodiment. A slight angle
variation was generated by the left clamp plate being
shorter to provide space for a fitting connecting the
fluid bladder to the lower pressure connection.
In other modifications, the bladder 314 can be a
section of gum rubber tube of 0.64 cm (0.25 in) outside
diameter and 0.30 cm (0.12 in) inside diameter, located
between the side stationary support 304 and the top
plate 306. Because the c~ie force was nonlinearly
related to the tube compression by the stationary
support, the stationary support position became much
more important. Alternatively, the bladder 314 can be
a small automotive carburetor accelerator pump
diaphragm with an effective diameter of about 2.8 cm
(1.1 in).
The die loading force can be generated by a single
continuous linear member such as a bladder or multiple
discrete low friction devices placed along the die
length. Similarly, the die support may be a single
unit or multiple units, as desired, for the die length.
Also, when a coating die is supported by a low friction
mount that is actuated with small forces, the flexible
liquid feed supply to the die can create unwanted
forces that can either add to or subtract from the
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actuation force. The design of an effective system
should carefully locate the feed hoses to prevent
unwanted variability of the die force against the web.
A swing arm floating mounting system 400 having
three degrees of freedom is shown in Figure 4. In this
embodiment, a fixed arm 402 is fixed to a slide 404.
The slide 404 has a dovetail cutout 406. One or more
slides 404 can be adjustably located at various
locations along a rail (not shown) to position dies 10
in desired transverse locations to coat a surface. A
bladder mount 410 is fixed to a top surface 412 of the
slide 404. A swing arm 414 is pivotably mounted to the
fixed arm 402. The swing arm 414 has a top surface
416 which receives a coating die 10 and a perpendicular
surface 418 which faces the bladder mount 410. As
shown, a flex member 420 connects the swing arm 414 to
the fixed arm 402. The flex member 420 can be
0.0254 cm (0.010 in) thick stainless shim stock clamped
between vertically separated clamp plates 422 0.3175 cm
(0.125 in) apart. Bladders 424 can be located at any
point between the swing arm 414 and the fixed arm 402,
and between the bladder mount 410 and either the swing
arm 414 or the coating die 10.
The coating die l0 is mounted on the top surface
416 of the swing arm 414. The pivot point of the swing
arm 414 is about 14 cm (5.5 in) below the die parting
line. In one configuration, the mount is set with the
die 10 contacting the web at about the midpoint of the
swing arm 414 stroke. The die can ride over splices
and wrinkles in the surface being coated. From the
midpoint of the stroke, the die angle changes about +/-
0.9°. Different bladders 424 were used: a polyester
tube bladder was located in four different locations, a
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gum rubber tube in several locations, and an
accelerator pump diaphragm in two locations.
In one version, a polyester tube had a lower end
near the flex plate and extended upward for about 10 cm
(4 in) between the fixed arm and the adjacent side of
the swing arm. This required higher air loading
pressures because the lever arm ratio was about 0.36.
With the bladder positioned horizontally, parallel to
the die lips between the fixed arm and the swing arm
just below the top of the fixed arm, the die coated
effectively at a lever arm ratio of about 0.72. With
the bladder located between the die 10 and the bladder
mount 410, its major axis was parallel to the die lips.
The effective lever arm ratio was close to 1.0 and
continuous coating could be achieved at lower minimum
pressures.
Using the horizontal gum rubber tube, longer or
shorter pieces of tubing changed the tube spring
constant and the generated force for the same
deflection. This made the position of the fixed arm
more important, because the force generated on the
coating die was nonlinearly related to the compression
of the tube. The tube was also located between the
bladder mount 410 and either the die 10 or the top of
the swing arm 414. Metal or polymer springs placed
between the fixed arm 402 and the swing arm 414 can
accomplish the same function. The spring function
could also be combined into the flex member 420 by
making it with a higher spring constant. These
approaches increase the importance of the relative
position of the swing arm to the stationary member.
When the flex member contribution to the overall force
is kept small, the low friction actuator becomes the
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dominant mechanism for producing consistent coating
force against the die and a pressure setting to the
actuator is easily quantified.
To examine the effect of allowing the die to
rotate about a vertical axis, the standard flex clamp
plates with a uniform gap between them were replaced
with a pair that had the same gap in the center, with
the gap increasing linearly to each edge of the flex
member. The reduced constraint at the edges permitted
the die to rotate side-to-side with very little force.
This may be useful if the surface presented to the die
for coating is out of parallel with the fixed arm or
stationary support.
Figure 5 is a modification of the swing arm system
of Figure 4. In this embodiment, a fixed arm 502~can
be fixed to a slide. A bladder 504 is mounted on the
top surface 506 of the fixed arm 502. A swing arm 508
is pivotably mounted to the fixed arm 502. The swing
arm 508 has a top surface 510 which receives a coating
die 10 and a perpendicular, elongate portion 512. It
also includes a force-generating arm 514, which is
perpendicular to the elongate portion 512. The force-
generating arm 514 is rigidly connected to the elongate
portion 512 and a flex member 516 connects the swing
arm 508 to the fixed arm 502. The location of the flex
member 516 is shown as between the elongate portion 512
and the force-generating arm 514. As the bladder 504
pressure increases it moves the force-generating arm up
in Figure 5 and this pivots the elongate portion 512
toward the left to adjust the die.
An opening 518 in the force-generating arm 514
allows the fluid feed hose 520 (or other conduit) to
pass through and reach the die 10 to feed fluid to the
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die. The fixed arm 502 is surrounded by an enclosure
522. The enclosure 522 prevents unwanted production
environment material and other debris from interfering
with the mounting system. The fixed arm 502 and the
enclosure 522 also have openings 524, 526,
respectively, which permit the feed hose 520 to pass
through. The gap between the swing arm 508 and the
enclosure 522 could be sealed with rubberized fabric to
prevent rigid or viscous material from lodging in the
gap and degrading long term operability. Similarly,
any gap between the feed hose and the opening 526 in
the enclosure 522 should be sealed. (Alternatively,
the opening 526 can be larger and a sealing tube can
connect the enclosure 522 and the fixed arm 502 to
prevent spilled material from contacting the various
components of this system 500.) This design has a
lever arm ratio of about 0.85. The minimum loading
pressure to achieve continuous coating was comparable
to previous examples.
In Figure 6, the mounting system 600 is enclosed
by an enclosure 602. In this embodiment, the entire
enclosure serves as the moving member. The enclosure
602 is connected to a stationary member 604 by a
flexible member 606. The bladder 610 located near the
top of the stationary member 604 adjacent the die 10
has a lever arm ratio of approximately 0.72. The
enclosure protects the fluid feed hose 608 as well as
the fluid bladder 610 and prevents unwanted production
environment material and other debris from interfering
with the movement of the die.
The feed hose 608 delivering fluid to the coating
die 10 can add or subtract force from the mount or
twist the flex member 606. This is due to the
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connection internal pressure, location, stiffness,
orientation, tension along its length, and centerline
path and creates an unknown force on the die. This can
be reduced by fastening the hose 608 to the enclosure
602 closer to the flex member 606, reducing the
effective lever arm length for the feed hose 608.
Also, fastening the other end of the feed hose 608
further from the die 10 reduces the likelihood that
bumping or other mechanical upsets will affect the
coating quality.
A further modification to the bladder design is to
use dual bladders concentrically mounted to an axis
perpendicular to the swing arm. The bladders can be
clamped at their outer periphery to the fixed base and
separated by a spacer ring. A stepped center plug is
located at the inner periphery of each bladder.
Introducing pressurized fluid between the diaphragms
creates a driving force toward the side with the
bladder of the larger area to move the swing arm.
For the swing arm systems, the center of mass of
the coating die and mount is located roughly along a
vertical line above the flex member. When coating
against a roll at the horizontal tangent point, the die
force against the web will be influenced only slightly
by the horizontal offset between the mass center and
flex member. If the coating assembly is rotated
counterclockwise around the roll surface, the die and
swing arm assembly mass center horizontal offset from
the flex member will increase, adding the die-mount
mass to the force at the die lip. Conversely if the
coating assembly is rotated clockwise around the roll
surface, the die and swing arm mass center will be to
the right of the flex member and the die-mount mass
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will subtract from the force generated by the bladder.
To varying degrees this is true for the other mounting
systems. The same is true fox free span coating.
The flex members in the designs described are
largely in compression. A thinner flex member would
have an increased tendency to buckle. Loading the flex
members in tension such as when the stationary member
is above the coating die will eliminate the tendency to
buckle and would reduce the influence of the flex
member spring constant on the die force.
Each mounting system has different features that
are appropriate for different coating conditions.
Restricting degrees of freedom reduces dynamic
interactions. This reduces the complexity, increases
robustness, and matches the dynamics of the mount to
that of the coating system. The knife edge mounting
system of Figure 1, has three degrees of freedom, and
has very little stiffness and springiness to resist
motion or dampen vibrations. The compound flexure
mounting system of Figure 2 has only one degree of
freedom, no moving bearing surfaces to wear, and
inherent spring, mass, and damper parameters that could
be selected to dampen vibrations. The flexure mounting
system of Figure 3, with two degrees of freedom and a
simple design, is easy to construct from components.
The swing arm mounting systems of Figures 4-6 eliminate
one of the flexures. They can twist or rotate about
the z axis and orient the die to the face of the web.
The swing arm mount has three degrees of freedom, is
simple and robust, and easy to manufacture.
Various changes and modifications can be made in
the invention without departing from the scope or
spirit of the invention. These die mounting systems
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can be modified by reducing their mass and by forming
them as monolithic mounts machined from a single piece
of metal or other material. Also, the mounting systems
and the dies can be oriented in different positions
5 depending on the coating setup. All materials cited in
this disclosure are incorporated by reference.
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